Flavor and Aroma Biology

Transcription

1 Flavor and Aroma Biology utline Introduction to our sensory system and the perception of flavor Florence Zakharov Department of Plant Sciences David benland USDA/ARS Relationships between fruit composition and flavor perception Fruit biology and development of flavor components (influence of genetic and environmental factors) Perception of Quality Perception of Quality ur sensory systems are responsible for generating an internal representation of the outside world, including its chemical (taste and olfaction) and physical (mechanical, sound, vision and temperature) features. When evaluating the quality of the foods we eat, we use the complete array of our sensory system (chemical and physical senses) and integrate this information to formulate a judgment. Varies depending on protagonist in PH chain Consumer-centric quality ultimately drives marketability and sales verall consumer acceptance (and repeat buy) strongly correlated with Flavor acceptance From an evolution standpoint, chemical senses are the most primal of the senses. Sensory Attributes of Foods Appearance Taste dor/smell/aroma Irritation/pain Texture/mouthfeel Temperature ur sense of taste is in charge of evaluating the nutritious content of food and preventing the ingestion of toxic substances. Taste is a sensation perceived in the mouth, more specifically on the tongue. We have innate likes and dislikes for it. Sweet Salty Bitter Sour (acidic) Taste 5 TASTE MDALITIES Umami (protein savory) 1

2 Fruit Composition and Taste Quality Class of compound Examples Sweet Sugars Sucrose, fructose, glucose Some proteins Monellin, thaumatin Sour Acids Citric acid, malic acid, tartaric acid Texture and Mouthfeel Astringency (tannins, calcium oxalate) Sense of touch (mechanoreceptors) Bitter Alkaloids, Phenolics, Terpenoids, some proteins Naringin, cucurbitacins, limonoids Salty Ions Sodium, calcium Umami Amino acids Glutamate, aspartate Aroma (or smell or odor) is the sensation perceived when volatile compounds are drawn into the nose. Aroma We have learned likes and dislikes for it. Taste and Aroma Taste and aroma are very closely linked. If you want to only TASTE something, you need to pinch your nose to avoid perceiving the volatiles in foods or drinks. What is a volatile compound? H CH2 CH3 CH2 methylsalicylate phenylethanol H benzaldehyde CH3 eugenol H A small molecule which has a high tendency to evaporate. limonene phenylacetaldehyde CH2 phenylacetaldehyde Volatiles are naturally produced by plants (flowers, fruits, vegetables, herbs ) and animals. They can also be made artificially (by chemical reactions designed for their production). CH2 phenylethanol nerolidol neral geranial limonene CH 2 geraniol phenylethanol 2

3 What does a volatile compound smell like? Each single volatile compound has a distinct smell. Character-impact volatiles Vanillin H 2-isobutyl 3-methoxypyrazine CH 3 -ionone Dimethyl disulfide Myrcene N N S S CH 3 Floral, woody, sweet, fruity, berry, green Sulfurous, vegetable, cabbage, onion Peppery, spicy Complexity of Fruit Aromas A natural aroma, smell or odor is typically made up of tens or sometimes hundreds of different volatile compounds. A mixture of volatile compounds is not perceived as the sum of its parts : volatiles interact to create a unique, distinct, aroma. The aroma of a strawberry ver 200 volatile compounds!! GC olfactometry is used to help determine which volatiles contribute to flavor Tomato GC lfactometry chromatogram hexanal cis-3-hexenal trans-2-hexenal methional 1-octen-3-one 6-methyl-5-hepten-3-one 2-isobutylthiazole phenylacetaldehyde furaneol methylsalicylate citral E,E-2,4-decadienal geranylacetone beta-ionone Elizabeth Baldwin, USDA/ARS 3

4 dor Thresholds What the nose knows We have different sensitivity levels for different volatiles. Some volatiles, like furaneol, can be detected by our olfactory system at extremely low levels; while others, like acetic acid (vinegar!), we can detect only at higher T 60 ppm levels. Even though acetic acid is much more abundant than furaneol in strawberries, it is furaneol that is more important for determining the characteristic aroma of the strawberry (because of its low odor H threshold value). T 10 ppb Studying Fruit Flavor What kinds of flavor compounds are present in fruits? How do plants produce these flavor compounds? How do internal and external factors influence the production of these compounds? Define commodity- and variety-specific compositional characteristics that can be related to sensory attributes Develop varieties with novel flavor properties based on knowledge of genetic determinants of volatile formation Control fruit flavor quality throughout production and postharvest handling C 2 Calvin Cycle Sugars Sugars Glycolysis Flavor Development: Diversity and Complexity Genetic factors A B C D E Pathways, hormones, regulatory mechanisms J F G H I Climactic factors Temperature, light, atmospheric gases R Q Volatiles More carb. Pigments Acids Proteins K L M N P Agricultural factors Soil type, irrigation, fertilization Taste Development Sugars Starch accumulation is an important factor for determining the final sugar content of many fruits. In tomato, cultivars that accumulate higher levels of starch in young fruits eventually contain more soluble sugars at the ripe stage. Sugars from leaves (photosynthesis) Starch in the fruit Starch in the fruit Soluble Sugars (sweet) Soluble Sugars (sweeter) Aroma Development Volatiles How are aroma volatiles made in plants? There are more than 2,000 volatiles known to date in plants. About 900 different volatiles have been reported in fruits and vegetables. Research has identified genes involved in the synthesis of less than 10% of all volatiles known. 4

5 R 1 Alcohol Acyl Transferase: a gene involved in fruit aroma formation VAAT + S SAAT CoA + R 2 CM-AATs R 2 BanAAT AAT (Aroma) Alcohol Acyl-CoA Volatile Ester R 1 HS CoA CoA Aroma Development Volatiles How is aroma (volatile) production controlled in fruits/vegetables? In climacteric fruits, ethylene plays an important role in triggering aroma formation during fruit ripening. ctyl Acetate Hexyl Acetate Regulation of Aroma Formation Regulation of Aroma Formation Ethylene Aroma-forming gene Normal Transgenic Ayub et al., 1996 El-Sharkawy et al., 2005 Aroma Biology What are the impacts of cultivation practices and postharvest storage on aroma formation? Pre-harvest factors Supply of carbon (sugars) to the fruit, water stress, light, temperature, plant diseases Postharvest factors Temperature Aroma Biology Cold slows down metabolism (less volatiles made). Cold slows down evaporation of volatiles from fruit surface. Ethylene In climacteric fruits, aroma cannot form without ethylene. Modified or controlled atmosphere MA or CA alters plant metabolism risk of anaerobic metabolism which can cause off-odors. 5

6 An example of the impact of temperature on flavor mandarins Modified atmospheres can form within fruit as a result of coating application 8 7 Hedonic score Some taste panel comments on warm temp fruit Spoiled, rancid Really old ff-flavor Strange aftertaste Not fresh ver ripe 68 F 41F 0 weeks 2 weeks 4 weeks Weeks after packing Warm temperature main cause of flavor loss Time in cold storage influences response Waxed Unwaxed Effect of modified atmosphere as a result of surface coating on mandarin ethanol concentration Harvest ethanol Coating + 68 F 1 week ethyl esters Quality-oriented practices Is there hope?... Understand the physiology of commodity, select cultivars with optimum flavor quality. Harvest at maximum flavor potential (riper) to attain (and retain) maximum flavor quality. More Research needed Improving techniques to slow down metabolism when fruits already start to ripen. Developing rapid, non-destructive methods for objective flavor quality determination (beyond Brix ) 6